This invention relates to electronic integration systems which generate output signals corresponding to the integral of input signals over a period of time. The invention further relates to the measurement forces as a function of time, and to the generation of electrical signals according to the value of measured forces. The invention relates further to electronic ski binding systems, wherein a safety binding may be placed in a released condition upon the generation of electrical signals reflective of the occurrence of forces which could cause injury or damage.
Electronic integrating circuits are well known wherein an output signal is generated corresponding to the integral of an input signal over a predetermined period of time. For example, a basic electronic integrating circuit may include an operational amplifier having a resistance load at an input port, a capacitive load connected across the amplifier, and an output port. A reset switch is ordinarily provided for discharging the capacitor to enable repetitive integrations from a preselected reference. The parameters of these known integrators may be expressed mathematically as follows: ##EQU1## where
V.sub.o =output voltage
V.sub.in =input voltage as a function of time
R=resistance
C=capacitance
t=time
Such integrating circuits are discussed in the following publications: "Analog Computer Techniques" by Clarence Johnson; published in 1956 by McGraw-Hill Book Company, Inc.--pages 3, 37, 59, 60, 61, 85, 89, 196; "Handbook of Operational Amplifier Applications" by Burr-Brown Research Corporation, copyrighted in 1963 by Burr-Brown Research Corporation--pages 50-53; "Applications Manual for Operational Amplifiers" by Philbrick/Nexus Research, published 1969 by Philbrick/Nexus Research--sections II. 10, II. 11 and II. 12; "System Engineering Handbook" edited by Robert E. Machol in collaboration with Wilson P. Tanner, Jr. and Samuel N. Alexander, published by McGraw-Hill Book Company--pages 10-6, 10-8.
Electrical systems for actuating safety ski bindings have been in the course of development over the past few years. These systems basically provide for the generation of electrical signals in response to the occurrence of forces, and for the generation of a release signal for actuating a trigger mechanism to release the binding when the electrical signals exceed some predetermined threshold value which is intended to reflect a danger condition. Such systems are disclosed, for example, in U.S. Pat. Nos. 3,762,735 (Smolka), 3,774,922 (Smolka), 3,776,566 (Smolka) and 3,892,980 (Anderson). A mechanically operated switch closes a circuit to actuate a release solenoid in U.S. Pat. No. 3,367,672 (Tonozzi et al). German Patent Publication OLS No. 201,4935 (Agerer) describes a ski binding whose release setting is controlled by a computer according to various operating conditions. Another German Patent Publication OLS No. 2,049,994 (Pistol) provides a binding with an electrical release binding actuable by a foot switch or handle.
In some of the foregoing electrical ski binding release systems, the time characteristics of applied forces are also included in the measurements made to control actuation of the release mechanism. Accordingly, U.S. Pat. No. 3,907,317 (Marker et al) discloses an electrical ski binding release system including circuitry for measuring the mean value of applied forces taken over a period of time, and for effecting release of the binding when that mean value exceeds some threshold value. In another system described in U.S. Pat. No. 3,919,563 (Lautier et al), electrical signals corresponding to the magnitudes of applied forces are integrated over predetermined time periods, and the integrated signal is compared to a referenced value which is a threshold of release.
German Patent Application No. P 2721691 (Salomon) discloses an electrically operated ski binding having an electronic control system wherein electrical signals corresponding to sensed forces are damped inversely according to the duration of the signal on the hypothesis that the skier's leg can stand high forces for short periods but not for extended periods. In German Patent Application No. P 2726143 (Salomon), another ski binding control circuit is disclosed in which an electrical signal corresponding to sensed forces is compared to a variable threshold value, the variance being inversely proportional to the duration of the signal. The latter circuit transforms the input signal from an analog signal to a digital equivalent, and the digital signal is measured against the threshold value which is decreasing with time. Another electronic circuit for a ski binding release system is described in German Patent Application No. P 2736027 (Salomon), wherein a threshold of release against which processed input force signals are compared is automatically adjusted during skiing according to forces sensed during skiing.
In co-pending U.S. patent application Ser. No. 467,821 filed May 7, 1974, an electrical release system is disclosed wherein forces are transduced into electrical signals which are processed in an integrating circuit and in a time delay circuit. The respective output signals are compared with threshold reference signals, and a release signal is generated when the output of either the integrating circuit or the delay circuit exceeds the threshold value.
Another system incorporating integrating circuitry is discussed in U.S. Pat. No. 3,701,903 (Merhar) wherein a piezoelectric sensor in a vehicle generates electrical signals in response to impacts upon the vehicle, and the signals are processed in a voltage limiter and then processed in an integrating circuit. A detection circuit responsive to the integrated signal activates a passenger restraining system.
To the extent that the foregoing systems incorporate integrating networks for generating electrical signals to be processed in decision making circuitry, the integration is performed using fixed integrating parameters; that is, the time constant of integration is a constant in each case.